A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM) such as carbon fiber paper, which facilitates a delivery of reactants such as hydrogen to the anode and oxygen to the cathode. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
As is well understood in the art, the membranes within the fuel cell stack must have a certain relative humidity (RH) for efficient performance. Measures are often taken to maintain the membrane hydration within a desired range that optimizes proton conduction across the electrolyte membranes. In a common approach, at least one of the reactants is directed to a membrane humidifier or water vapor transport (WVT) device before they are directed to the fuel cell. For example, humidification of the fuel cell is discussed in commonly owned U.S. Pat. No. 7,036,466 to Goebel et al., commonly owned U.S. Pat. Appl. Pub. No. 2006/0029837 to Sennoun et al., and commonly owned U.S. Pat. Appl. Pub. No. 2005/0260469 to Forte, each of which is hereby incorporated herein by reference in its entirety. WVT devices are commonly used to humidify air directed to the cathodes of the fuel cell stack. Examples of air humidifiers are shown and described in U.S. Pat. No. 7,156,379 to Tanihara et al., hereby incorporated herein by reference in its entirety, and U.S. Pat. No. 6,471,195 to Shimanuki et al., hereby incorporated herein by reference in its entirety. The WVT device may be either external to the fuel cell stack or may be formed within the fuel cell stack.
A typical membrane humidifier-type WVT device is disclosed in commonly owned U.S. Pat. Appl. Pub. No. 2008/0001313 to Zhang et al., hereby incorporated herein by reference in its entirety. The membrane humidifier includes a substantially planar first plate having at least one substantially linear flow channel formed therein, and a substantially planar second plate having at least one substantially linear flow channel formed therein. The flow channels of the first and second plates facilitate a flow of a first and second gas therethrough, respectively. A diffusion medium is disposed between the first plate and the second plate and is adapted to permit a transfer of water vapor therethrough. A membrane is also disposed between the first plate and the second plate and is adapted to permit a transfer of water vapor therethrough. The water vapor in the first gas is transferred through the diffusion medium and the membrane to the second gas.
There is a continuing need for a fuel cell system with a water vapor transport device that maintains mechanical strength and stability in relation to creep, thermal expansion, and hydro expansion of the membrane of the water vapor transport device. Desirably, the water vapor transport device exhibits through-plane stiffness sufficient to absorb membrane expansion during operation of the water vapor transport device.